Views: 0 Author: Site Editor Publish Time: 2025-11-05 Origin: Site
Bag Air Filter is the most common "medium-efficiency" or "sub-high-efficiency" stage filter for central air conditioners, air handling units (AHUs), cleanroom air conditioners, constant temperature and humidity systems, and desiccant rotors. Gezi Filtech Manufacturing Co., Ltd. has extensive applications in industries such as central air conditioning, cleanrooms, pharmaceuticals, electronics, and food processing. By increasing the number and depth of filter bags, the filtration area is expanded exponentially, achieving high dust-holding capacity, low pressure drop, and long service life. The following content is compiled based on the latest public data in 2025 and can be directly used for selection, procurement, and maintenance.
1. Primary/ Medium Efficiency Bag Filter Working Principle
Dust-laden air flows from the outside to the inside of the filter bag. Dust is captured by the fiber layer through interception, inertial impaction, diffusion, and electrostatic adsorption. Clean air passes through the filter media into the bag and is then discharged. As the dust layer thickens, the pressure drop rises to the "final resistance", at which point the filter should be replaced.
2. Mainstream Grades and Efficiency Comparison (EN 779:2012 + GB/T 14295-2019)
Grade | 0.4 μm Efficiency | Weight Efficiency | Common Stage | Final Resistance for Replacement |
F5 | 40–60% | ≥ 90% | Pre-medium Efficiency | 250 Pa |
F6 | 60–80% | ≥ 95% | Medium Efficiency | 300–450 Pa |
F7 | 80–90% | ≥ 98% | Medium-high Efficiency | 450–600 Pa |
F8 | 90–95% | ≥ 99% | Sub-high Efficiency | 600 Pa |
F9 | ≥ 95% | ≥ 99.5% | Sub-high Efficiency | 600–800 Pa |
F7/F8 correspond to MERV 13–14 in ASHRAE 52.2; F9 is close to MERV 15.
3. HEPA Filter BagCore Selection Parameters
1. Airflow Rate and Face Velocity
Rated airflow rate: 500–6,000 m³/h.
Optimal face velocity: 0.8–1.8 m/min. Excessively high velocity shortens service life, while excessively low velocity wastes space.
2. Initial/Final Resistance
New bag resistance: 60–120 Pa.
Recommended final resistance: 300–600 Pa (for F6–F9). Exceeding this value leads to a sharp increase in energy consumption.
3. Dust-Holding Capacity
F6: ≥ 300 g; F8: 500–1,200 g.
For the same grade, dust-holding capacity follows: glass fiber > composite > polyester. However, glass fiber is brittle and more expensive.
4. Bag Air Filter Media Selection
Polyester (PET): Low cost, moisture-resistant, washable, temperature resistance < 100 °C. Preferred for ordinary commercial air conditioners.
Polypropylene (PP): Hydrophobic, mildew-resistant. Suitable for high-humidity environments in food and pharmaceutical industries.
Glass Fiber: High temperature resistance (260 °C) and high efficiency, but brittle and prone to fiber shedding. Mostly used for high-temperature flue gas or cleanrooms.
Composite Electret: Combines electrostatic adsorption and fiber filtration. Improves 0.4 μm efficiency by 10–15% and extends service life by 30% under the same pressure drop.
5. Number and Depth of Bag Filters
Common bag counts: 6 bags, 8 bags.
Common bag depths: 300 mm, 400 mm, 550 mm.
Depth is proportional to filtration area and service life, but slightly increases initial resistance.
4. Bag Air Filter Typical Structure
Outer Frame: Galvanized steel sheet (economical), aluminum alloy (lightweight, corrosion-resistant), stainless steel (for high-humidity/high-salt environments).
Support: Metal separators or ultrasonic welding. Prevents bag walls from adhering under high wind speed, which would reduce effective filtration area.
Sealing: Integrally formed EVA or PU gasket. Ensures no bypass leakage with the unit guide rail.
5. Bag Filter Usage and Maintenance
Cycle | Action |
Daily | Monitor the differential pressure gauge and record ΔP. |
1–3 Months | Check the integrity of the frame and sealing strip. |
6–12 Months | Replace the entire filter pack when pressure drop reaches final resistance or efficiency decreases (non-washable). |
During Replacement | Handle with care to avoid secondary dust emission from vibration. Seal used bags in containers for centralized disposal. |
6. 3-Step Quick Selection Method
Check Stage Position: Pre-medium efficiency (F5/F6) protects end high-efficiency filters; sub-high efficiency (F8/F9) can be directly used as the return air end for cleanrooms.
Check Environment: Choose PP or coated media for high-humidity/food/pharmaceutical environments; glass fiber for high-temperature flue gas; PET for ordinary air conditioners.
Check Energy Consumption: For the same efficiency, select models with initial pressure drop 10–20 Pa lower. This can save 5–8% of annual electricity costs for large-airflow systems.
7. Price Reference (2025, Domestic Made)
Grade | 6-Bag (592×592×550 mm) | Unit Price (USD/Unit) |
F6 | Polyester | 72–100 |
F7 | Composite | 100–130 |
F8 | Glass Fiber | 130–175 |
F9 | Electret | 175–225 |
For large orders or customized extended sizes (635 mm), prices can be reduced by 10–15%.
Stainless steel frames add approximately 30% to the price.
If you need:
Combined resistance calculation for FFU and high-efficiency air supply outlets
Selection table for high-temperature (260 °C) glass fiber bag filters
Verification template (interpretation of EN 779 test reports)
Please provide specific airflow rate, grade, or application scenario, and Gezi Filtech Manufacturing Co., Ltd. will continue to refine the solution for you!
